Hypersonic Weapons: An Idea So Crazy It Just Might Work

Last month, Guy Norris reported for Aviation Week & Space Technology on how the Chinese government has revealed a national plan for hypersonic aircraft research. On this side of the Pacific, people have been getting stressed. Norris's earlier report in February covered a classified assessment within the US government that warned of possible breakthroughs in Chinese hypersonic technology, and of how American efforts were “lacking urgency.” Norris, Joe Anselmo, and Graham Warwick even produced a Check Six podcast episode on the issue. But during the previous administration, the Army, Navy, and Air Force Departments did all seem to be talking up new ideas for fast-moving weapons. So does the Pentagon need to be putting more money there? Does any other defense ministry? Perhaps, but sometimes necessity is truncated by feasibility. For with hypersonics, the tactical advantages are great, but so are the technical challenges.

There are at least three ways to make weapons go hypersonic: making a missile that flies very fast, firing a very skinny projectile with a discarding sabot from a cannon, or just firing a projectile from a railgun. As Norris noted, American research on hypersonic missiles has been underway in “starts and stops” since 1947. Tank guns have been firing discarding sabot rounds since the 1940s. When “the long rod” exits the barrel of Rheinmetall’s famous 120 mm L/44 or L/55, the main guns for Abrams and Leopard 2 tanks, it’s moving at about Mach 5. Not much stands in the way of that. It’s perhaps no surprise that Will Roper's Strategic Capabilities Office at the Pentagon has recently gotten enthused about equipping longer-range naval guns with even longer-range “Hyper-Velocity Projectiles” (HVPs). Railguns have been discussed for decades; of late, BAE Systems and General Atomics have each been working on prototypes, and DRS has been working on the necessary power systems.

For this reason, the Wall Street Journal recently called the Navy’s proposed Mach 7 railgun projectile a “battlefield meteorite with the power to blow holes in enemy ships and level terrorist camps.” (After all, in The Expanse, when the Martians divert power to the railguns, you know they're getting serious.) However one attains those kinds of velocities, the kinetic energy alone is enough to do great damage. Hypersonic weapons are also very difficult to intercept; just note the herculean efforts expended on anti-ballistic missile defense: shooting the things down is considerably more expensive, and that leads to unfavorable economics against the inbounds. But for all that awesomeness, there are at least eight serious issues with going so very fast.

Shock. Launching a projectile to Mach 7 over a militarily useful barrel length means accelerating the little guy at 20,000 times gravity. That’s several times what cannon rounds experience in conventional guns. Plenty of munitions makers—Raytheon, Lockheed Martin, Alliant Techsystems, Leonardo, Rheinmetall, Denel, etc.—have learned to shock-harden the electronics of precision-guided shells to the lesser extreme. As the Navy is still looking for sources of supply, shock-hardening railgun and chemically-propelled long darts is apparently proving a bit more challenging.

Sensing. At high Mach numbers, aero-structures become encased in plasma sheaths—envelopes of disassociated nuclei and electronics, of high conductivity, that interfere with all electromagnetic transmissions. Think about how many astronaut movies feature those tense few minutes when mission control can’t talk to the capsule during atmospheric reentry. Making missiles or munitions that don’t fly blindly hypersonically requires datalinks and sensors that can operate through that mess. The US Air Force started looking for a way to address the problem in the late 1950s. It’s still far from solved.